This invention relates to a pneumatic radial tire for a truck or bus, which mitigates the shoulder wear without sacrificing the wet-grip performance.
Generally, the radial tire for use on a truck or a bus is provided with a carcass formed of cords which are substantially perpendicularly arranged to the equatorial plane of tire and a steel cord belt layer which is interposed between the carcass and the tread of the tire. Since a radial tire is supenion to a bias ply tire in terms of abrasion resistance, puncture resistance, and fuel consumption, it is notably gaining popularity in recent years. In radial tires, however, the shoulder parts offer lower rigidity than the tread center and are liable to produce more relative motion, since the belt layer of high rigidity is disposed in the crown part of the tire. Such a radial tire suffer from more advanced abrasion against the road surface. Thus, the so-called shoulder abrasion, i.e., a phenomenon in which the wear of the tread of a tire proceeds more quickly in the shoulder parts than in the tread center, inevitably ensues.
In the meantime, all-season tires used for travel on wetroads including snow-covered roads prevalently adopts a block tread pattern. A block tread pattern, when used in the tire under a heavy load such as that of a truck or a bus, offers intolerably low abrasion resistance. Thus use of a tire incorporating a block tread pattern under such conditions generally proves high uneconomical.